Double edged sword of DDT

This (Feb 2o17) article is a worthwhile read and relevant to Gene-Environment Interactions.

“Too much of a good thing –– is not necessariily a good thing.”

The Double-Edged Sword of DDT

On Jan. 24, 2017, PBS aired a two-hour special on Rachel Carson, the “Mother of the Environmental Movement.”

Rachel Carson for sure was an American hero. In the early 1960s, she was the first to warn that a pesticide called DDT could accumulate in the environment, the first to show that it could harm fish, birds, and other wildlife, the first to warn that its overuse would render it ineffective, and the first to predict that more natural means of pest control — such as bacteria that killed mosquito larvae — should be used instead.

November 1941, Rachel Carson published her first book, Under the Sea-Wind. Although written for adults, the book had a child-like sense of wonder. Under the Sea-Wind told the story of Silverbar, a sanderling that had migrated from the Arctic Circle to Argentina;Scomber, a mackerel that traveled from New England to the Continental Shelf; and Anguilla, an American eel that journeyed to the Sargasso Sea to spawn. “There is poetry here,” wrote one reviewer.

July 1951, Carson published her second book, The Sea around Us. Two months later, The Sea around Us became #1 on the New York Times bestseller list, where it remained for 39 weeks –– a record. When the dust settled, The Sea around Us had sold more than 1.3 million copies, had been translated into 32 languages, had won the National Book Award, and had been made into a movie. Editors of the country’s leading newspapers voted Rachel Carson “Woman of the Year.”

In October 1955, Carson published her third book, The Edge of the Sea, a tour guide for the casual adventurer. The New Yorker serialized it, critics praised it, and the public loved it: more than 70,000 copies were sold as it rocketed to #4 on the New York Times bestseller list.

Today, most people under the age of 40 have probably never heard of Rachel Carson. But in the early 1960s, almost every American knew her name.

September 1962, Rachel Carson changed her tone. Her next book, Silent Spring, which she called her “poison book,” was a bold article, warning against pesticides: especially DDT.

The first chapter of Silent Spring, titled ‘A Fable for Tomorrow,’ appealed to our sensea that human kind had sinned. “There was once a town in the heart of America, where all life seemed to live in harmony with its surroundings. Then, a strange blight crept over the area and everything began to change… the cattle and sheep sickened and died… streams were lifeless… everywhere there was the shadow of death.” Birds, especially, had fallen victim to this strange evil. In a town that had once “throbbed with scores of bird voices there was now no sound, only silence.” A silent spring.

Carson made it clear that she wasn’t talking about something that might happen — she was writing about something that had happened. Our war against nature had become a war against ourselves.

In May 1963, Rachel Carson appeared before the Department of Commerce and asked for a “Pesticide Commission” to regulate the untethered use of DDT. Ten years later, Carson’s “Pesticide Commission” became the Environmental Protection Agency, which immediately banned DDT. Following America’s lead, support for international use of DDT quickly dried up. Although DDT soon became synonymous with poison, the pesticide was an effective weapon in the fight against an infection that has killed — and continues to kill — more people than any other: malaria.

By 1960, largely due to DDT, malaria had been eliminated from eleven countries, including the United States. As malaria rates went down, life expectancies went up; as did crop production, land values, and relative wealth. Probably no country benefited from DDT more than Nepal, where spraying began in 1960. At the time, more than two million Nepalese suffered from malaria. By 1968, that number was reduced to 2,500; and life expectancy increased from 28 to 42 years.

After DDT was banned, malaria re-emerged across the globe:

• In India, between 1952 and 1962, DDT caused a decrease in annual malaria cases from 100 million to 60,000. By the late 1970s, no longer able to use DDT, the number of cases increased to 6 million.
• In Sri Lanka, before the use of DDT, 2.8 million people suffered from malaria. When the spraying stopped, only 17 people suffered from the disease. Then, no longer able to use DDT, Sri Lanka suffered a massive malaria epidemic: soaring to 1.5 million people infected by the parasite.
• In South Africa, after DDT became unavailable, the number of malaria cases increased from 8,500 to 42,000 and malaria deaths from 22 to 320.

Since the mid-1970s, when DDT was eliminated from global eradication efforts, tens of millions of people have died from malaria. Whereas it was reasonable to have banned DDT for agricultural use, it was unreasonable to have eliminated it from public health use. Environmentalists have argued that, “When it came to DDT, it was pick your poison. If DDT was banned, more people would die from malaria. But, if DDT wasn’t banned, people would suffer and die from a variety of other diseases, not the least of which was cancer.”

However, studies in Europe, Canada, and the United States have since shown that DDT didn’t cause the human diseases that Carson had claimed. Indeed, the only type of cancer that had increased in the United States during the DDT era was lung cancer –– which was caused by cigarette smoking. DDT was arguably one of the safer insect repellents ever invented — far safer than many of the pesticides that have taken its place.

Carson’s supporters argued that, had she lived longer, she would never have promoted a ban on DDT for the control of malaria. Indeed, in Silent Spring, Carson wrote, “It is not my contention that chemical pesticides never be used.” However, it was her contention that DDT had caused increases in risk of leukemia, liver disease, birth defects, premature births, and a whole range of chronic illnesses.

In 2006, the World Health Organization reinstated DDT as part of its effort to eradicate malaria –– but not before millions of people had died from the disease.

Additional facts: The author of this article should read the book, Silent Spring: “Sudden death” is mentioned once in Silent Spring, in relation to fish and crustaceans, and “aplastic anemia” is mentioned twice; in neither case is DDT the only (or, in fact, the likely) cause. “Birth defects” caused by DDT are not mentioned in Silent Spring.

“Liver disease” is mentioned, reflecting DDT concerns by the FDA, as early as 1950. “Chromosomal abnormalities” caused by DDT are not mentioned in Silent Spring. Some organic solvents used then are well known today to cause leukemia, so the only mention of a “DDT-related leukemia” in an adult is what it is in the book: a single case study. There is no mention in Silent Spring of a relationship between DDT and “women suffering infertility or uterine cancer.” Those who bother to read Silent Spring would know that Rachel Carson dealt not just with DDT –– but with other pesticides and environmental pollutants. The scientific knowledge of 1962 was not what it is now, and many of the “dangers” that she described as “potential” in 1962 are widely recognized today: chlordane, benzene, arsenic and parathion, to name but a few. But her concerns were not unreasonable at the time.

Claims by the article: “In India, between 1952 and 1962, DDT caused a decrease in annual malaria cases from 100 million to 60,000. By the late 1970s, no longer able to use DDT, the number of cases increased to 6 million.”

Additional facts: DDT use in India for malaria control was over 6,000 tons / year during the 1970s. Malaria resurgence caused an increase in DDT use to 9,000 tons in 1977. Malaria resurgence peaked in India in 1976 (~6.4 million cases), then decreased afterwards (to <4.1 million in 1978, and ~2 million in the 1990s). Malaria resurgence in the 1970s was not caused by any ban on DDT use. DDT is still in use in India today for malaria control –– although DDT use is limited by mosquito resistance.

Claims by the article: “In Sri Lanka, before the use of DDT, 2.8 million people suffered from malaria. When the spraying stopped, only 17 people suffered from the disease. Then, no longer able to use DDT, Sri Lanka suffered a massive malaria epidemic: soaring to 1.5 million people infected by the parasite.”

Additional facts: Use of DDT in Sri Lanka was started in 1945, when malaria was still endemic –– following the epidemic of 1934-35 with >5.5 million cases. It was stopped in April 1963 (i.e. long before the 1972 US ban on agricultural uses of DDT), when malaria had reached a low peak (17 cases of which six were indigenous). This stop was not a ban, but rather an operational decision. It was not considered cost-effective to continue the campaign with so few cases. As soon as this decision was proven wrong –– DDT spraying then resumed a few months later, and was continued unabated until 1977 when DDT was replaced by malathion –– because of resistance of the anophelines to DDT (but not because of a Rachel Carson-inspired ban). By 2013 all remaining (95) cases of malaria were imported. Sri Lanka has been malaria-free since 2016 (three consecutive years with zero local cases).

Claims by the article: “Since the mid-1970s, when DDT was eliminated from global eradication efforts, tens of millions of people have died from malaria unnecessarily.”

Additional facts: DDT was not eliminated from global eradication efforts in the mid-1970s. Worldwide malaria-related deaths peaked in 2004, despite the continued use of DDT (see below). In 2016, there were still 426,000 deaths globally and “Sub-Saharan Africa continues to carry a disproportionately high share of the global malaria burden. In 2015, the region was home to 90% of malaria cases and 92% of malaria deaths. Some 13 countries – mainly in sub-Saharan Africa – account for 76% of malaria cases and 75% deaths globally” (WHO fact sheet).

Claims by the article: “In 2006, the World Health Organization reinstated DDT as part of its effort to eradicate malaria –– but not before millions of people had died needlessly from the disease.”

Additional facts: In 2006 the WHO renewed its committment to the use of DDT. It did not “reinstate” DDT –– because it had never been completely “banned”. WHO stated in 2006 that “it is advisable to maintain the use of DDT, until a suitable alternative is available”(WHO/HTM/MAL/2006.1112). This had always been WHO’s policy, since 1971 (Official Records WHO 190: 176-182, 1971), and confirmed in 1995 (WHO Technical Reports Series 857): “There is no justification for changing current policy towards indoor spraying of DDT for vector control.”

This was further confirmed in 2011: “WHO recommends DDT only for indoor residual spraying. Countries can use DDT for as long as necessary, in the quantity needed, provided that the guidelines and recommendations of WHO and the Stockholm Convention are all met, and until locally appropriate and cost-effective alternatives are available for a sustainable transition from DDT. At its third meeting in May 2007, the Conference of the Parties of the Stockholm Convention concluded that there is a continued need for use of DDT in disease vector control”. (WHO/HTM/GMP/2011). Ten countries still use DDT for residual indoor spraying (WHO 2016 World Malaria Report). However, DDT is no longer considered the magic bullet against malaria –– as it may have been in the 1950s.

Claims by the article: “DDT was arguably one of the safer insect repellents ever invented — far safer than many of the pesticides that have taken its place.”

Additional facts: DDT was an incredibly safe insecticide, when discovered by Paul Muller, but all classes of insecticides –– that have replaced it since the mid-1970s –– have been even safer (Sparks, Pesticide Biochemistry and Physiology 2013; 107: 8-17). DDT is a persistent organic pollutant and has been phased out in agriculture. It will be phased out in public health, as well –– because there are cheaper, safer, and more effective alternatives.